| Evaporative air coolers are found in a wide range of applications, such as petrochemical plants and steel plants. A new type of evaporative air cooler also called film-increasing type evaporative air cooler (FITEAC) is developed in this paper. In the FITEAC, pieces of hydrophilic plates are placed in the spaces between a layer of tubes and another lower layer of tubes to change hot water falling from the upper layer of tubes into pieces of cooler water film. Placement of these hydrophilic plates enhances heat and mass transfer for the lower layer of tubes because temperature difference between the cooler water film and hot fluid inside the tubes is larger than that between hot water and the hot fluid.improved models for calculation of heat and mass transfer on the surfaces of plates and tubes were built in the paper. Temperature difference and moisture content difference are chosen as the driving forces correspondingly of heat and mass transfer and a system of specific difference equations (SSDE) is developed to solve easily the mathematical model for heat and mass transfer on plates and tubes. Based on traditional one-dimensional heat and mass transfer model for tubes, a two-dimensional model was built in the paper. In traditonal models, it is assumed that hot fluid parallelflows with water film out of tubes and the water film also counterflows with moist air, however, it is assumed that hot fluid crossflows with the water film in the model in the paper and heat transfer coefficient of air and water out of tubes varies with angles. So five variables varying independently which are temperature of air, moisture content of air, temperature of water film, mass flux of water film, temperature of hot fluid are distributed two-dimensionally in the plane made of horizontal axes of tube and vertical line and that is different with the traditional one-dimensional model in vertical direction sharply.Thickness of water film is a key factor for calculating heat transfer coefficient of water film out of tubes in an evaporative air cooler. A new method used to measure thickness of water film, called resistance method, was proposed in the test. Beacause resistance values of metal heat tubes, water film and air are very different, such as, that of metal heat tubes is about 10~6Ω, that of water film is about 100Ω, that of air is nearly infinity, thickness of water film can be measured by two electrodes which are set at a micrometer and a tube, and the precision of the mothod is 1μm. Thickness of water film at some angles on the surface of tube and on the surface of plate is measured by this method. Based on thickness of water film, a heat transfer coefficient model of water film was built.Capability of film-increasing plates for enhancing heat and mass transfer is validated in the tests. Main factors influencing heat and mass transfer in an evaporative air cooler was investigated by orthogonal tests. Effect of velocity of air, mass flow rate of water film, temperature of hot fluid on evaperative heat transfer was also explored in tests. Comparing heat transfer capacity of traditional tubes with that of the film-increasing tubes, it was find that the capacity of film-increasing tubes is 25% higher than that of traditional tubes for some cases.Existence, exclusive and astringency of two-valuabled silmple iterative equation and two-valuabled secant method was discussed for the case that two-valuabled iteratived equation curve is smaller than 1 and the iterative value is attenuation. Based on two-dimensional heat and mass transfer model built in the paper, a software is writed in MATLAB software to calculate heat transfer of an evaporative air cooler with multipass tubes. A specific iterative arithmetic is proposed and used in the software, which ties up fower EMS memory. The software is a efficient tool used to study heat and mass transfer performance of an evaporative air cooler.The present work is supported by the National Natural Science Foundation of China(No. 2007CB206901).
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